<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .circle {
            /* border: 2px solid #000; */
            width: 100px;
            height: 100px;
            border-radius: 50%;
            margin: 0 auto;
            --d: 60deg;
            /* 锥形渐变 */
            background: conic-gradient(#f00 var(--d), #0000 var(--d) calc(360deg - var(--d)), #f00 calc(360deg - var(--d)));
            transition: --d 1s;
        }

        @property --d {
            syntax: '<angle>';
            inherits: false;
            initial-value: 0deg;
        }

        .circle:hover {
            --d: 0deg;
        }
    </style>
</head>

<body>
    <div class="circle"></div>
</body>

</html>